The present invention relates to devices used to control the flow of fluid through vehicle fluid systems, such as a vehicle brake system.
For many people, when purchasing a motor vehicle, the way the car or truck handles is very important. Because of this, many vehicles are equipped with vehicle stability enhancement (VSE) control systems. Part of the function of VSE control systems is undertaken by an automatic braking system (ABS), which regulates the pressure within the vehicle wheel brake cylinders to maximize the stability of the vehicle while braking.
It happens that current ABS use several solenoid valves to control the flow of fluid between the component parts of the system. In order for the ABS to operate properly, a pump prime valve may be installed between a master cylinder/reservoir and a system pump.
When the brakes are applied, a relatively large pressure is generated within the pump prime valve. A spring within the valve keeps it closed until the control system energizes a coil that opens the valve. Due to the high fluid pressure across the valve when the brakes are applied, it is necessary that the spring which keeps the valve closed has a relatively large spring constant. The coil must be capable of creating a magnetic force that will overcome this spring force in addition to the hydraulic forces within the valve.
Accordingly, current solenoid valves must include a relatively large coil in order to overcome the force of the spring, which, in turn, results in a more expensive valve. A smaller, and less expensive, coil cannot be used in such valves because it would be incapable of providing the force necessary for opening the valve, without overheating or otherwise being damaged.
In light of the above problems, the present invention recognizes a need for a solenoid valve which is capable of operating under high braking pressures, while minimizing the size of the activating coil.
A two-stage parallel spring solenoid valve is configured for use in a vehicle fluid system and includes a coil housing with a coil disposed therein. Additionally, the valve forms a fluid communication path that is selectively blocked by a plunger assembly slidably disposed relative to the coil housing. The plunger assembly includes a plunger and a rod that are slidably received in the plunger. Moreover, disposed within the plunger assembly is an internal spring that urges the rod to move relative to the plunger and an external spring that urges the plunger to move relative to the housing. As such, the springs cooperate to move the plunger assembly to block the fluid communication path when the coil is de-energized and the coil is selectively energized to cause the plunger assembly to move to open the fluid communication path.
In a preferred embodiment, the two-stage parallel spring solenoid valve includes a hollow plunger tube that is disposed in the housing. The plunger tube defines a distal end and forms at least one port. Preferably, a valve body is disposed at the distal end of the plunger tube and includes a valve seat that circumscribes a fluid passage. The port and the fluid passage establish the fluid communication path. Also in a preferred embodiment, as described in detail below, the rod forms a ball that is configured so that it can mate with the valve seat. Moreover, a filter surrounds the distal end of the plunger tube and is juxtaposed with the inlet ports that are formed by the plunger tube. The valve body forms an o-ling groove and includes an o-ring disposed therein.
In another aspect of the present invention, a two-stage parallel spring solenoid valve includes a plunger tube that defines a distal end and a proximal end. A plunger stop is disposed within the proximal end of the plunger tube and a hollow valve body that forms a valve seat is disposed within the distal end of the plunger tube. Additionally, a plunger assembly is disposed within the plunger tube. In this aspect of the present invention, the plunger assembly includes a plunger rod that is slidably disposed within the plunger tube. The plunger rod is movable between a closed position, wherein the plunger rod engages the valve seat to block fluid flow through the valve and an open position, wherein the plunger rod is distanced from the valve seat.
In still another aspect of the present invention, a system for stabilizing a vehicle while braking includes a master cylinder, at least one wheel cylinder and a two-stage parallel spring solenoid valve that selectively directs hydraulic brake fluid to the wheel cylinders.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: